Can you define Epics and Stories on the graphical roadmap?

The graphical roadmap allows you to add "Lanes" of work and time dividers too - both are completely flexible to suit any methodology.

If you are using an agile development methodology, you can use the lanes to show "Themes" of work or "Epics" and you can add items in Receptive as User Stories where you can define the story, add attachments and facilitate discussion.